A date with Bogart
Spot the film icon McCalls are referencing in this dress pattern from 1956?
Ok, Ok, so that was an easy one. Now, having got that, which film inspired it?
Well, skimming the imdb entry for Audrey Hepburn shows that she starred in the film Sabrina in 1954 (at that time she had yet to make Breakfast at Tiffanys). Sabrina has some great costumes in it and is one of my favourite Hepburn films- great plot, great acting, great costumes. According to the Wikipedia entry on Sabrina:
Although Edith Head won an Oscar for Best Costumes, most of Hepburn’s outfits were in fact created by Hubert de Givenchy and chosen by the star herself. Edith Head refused to be shown alongside Givenchy in the credits, so she was given credit for the costumes, although the Academy’s votes were obviously for Hepburn’s attire.  Edith Head did not refuse the Oscar, however. The film began a life-long association between Givenchy and Hepburn (it has been reported that when Hepburn called on Givenchy for the first time in Paris, he assumed that it was Katharine Hepburn in his salon!) 
As this particular McCalls pattern is designed by Givenchy, I would say Sabrina is looking pretty conclusive as its inspiration, and my money would be on the dress below:
Here’s a kind of back view:
This is the dress that Sabrina wears on a date with Humphrey Bogart as he tries to win her away from his reckless younger brother to avoid disgracing the family (she is his chauffeur’s daughter after all).